Energy Extraction from a Black Hole by a Strongly Magnetized Thin Accretion Disk

TL;DR

This study uses 3D GRMHD simulations to explore how strong magnetic fields in thin accretion disks extract black hole rotational energy via the Blandford-Znajek process, affecting jet power, disk luminosity, and radiative efficiency.

Contribution

It provides new insights into energy extraction mechanisms in magnetized thin disks and their impact on jet formation and disk luminosity, contrasting with previous thick disk models.

Findings

The BH flux dependence on spin is weaker in thin disks.

Only 10-70% of BZ power powers jets, rest may drive winds or radiation.

Strong magnetic fields increase disk radiative efficiency and luminosity.

Abstract

The presence of a strong, large-scale magnetic field in an accretion flow leads to extraction of the rotational energy of the black hole (BH) through the Blandford-Znajek (BZ) process, believed to power relativistic jets in various astrophysical sources. We study rotational energy extraction from a BH surrounded by a highly magnetized thin disk by performing a set of 3D global GRMHD simulations. We find that the saturated flux threading the BH has a weaker dependence on BH spin, compared to highly magnetized hot (geometrically thick) accretion flows. Also, we find that only a fraction ($10-70$ per cent) of the extracted BZ power is channeled into the jet, depending on the spin parameter. The remaining energy is potentially used to launch winds or contribute to the radiative output of the disk or corona. Our simulations reveal that the presence of a strong magnetic field enhances the radiative efficiency of the disk, making it more luminous than its weakly magnetized counterpart or the standard disk model. We attribute this excess luminosity primarily to the enhanced magnetic dissipation in the intra-ISCO region. Our findings have implications for understanding X-ray corona formation and black hole spin measurements, and interpreting black hole transient phenomena.